SN 2006 bt：一颗令人困惑、麻烦且可能误导的Ia型超新星
SN 2006bt: A Perplexing, Troublesome, and Possibly Misleading Type Ia Supernova
摘要：
SN 2006 bt显示出与其他已知Ia型超新星（SN Ia）不同的特征。我们提出了SN 2006 bt的光学光变曲线和光谱，证明了这个物体的特殊性质。SN 2006 bt的光变曲线较宽且缓慢下降，这表明它是一个热的、高光度的SN，但在i波段没有像低光度的SN Ia那样的第二个最大值。它的光谱与低光度的Ia型超新星相似，包含只有在冷的SN光球中才有的特征。光变曲线拟合方法表明SN 2006 bt是由大量的尘埃变红的，然而，它发生在其早期型宿主星系的外围，并且在其光谱中没有强烈的Na-D吸收，这表明宿主星系的尘埃吸收量可以忽略不计。C II可能在我们的前极大光谱中被检测到，但速度比其他元素低得多。这颗恒星的祖先可能非常古老，是一个没有近期恒星形成迹象的星系的晕族成员。Ia超新星已经非常成功地被建模为一个单参数家族，这是它们作为宇宙学距离指标的基础。SN 2006 bt是对这一图景的挑战，但它相对正常的光变曲线允许SN 2006 bt被纳入宇宙学分析。我们生成模拟SN Ia数据集，这表明类似的对象的污染将增加散射的SN Ia哈勃图和系统的宇宙学参数的偏差测量。然而，光谱和静止帧i波段光变曲线应该提供一个明确的方式来识别和消除这些对象。
英文摘要：
SN 2006bt displays characteristics unlike those of any other known Type Ia supernova (SN Ia). We present optical light curves and spectra of SN 2006bt which demonstrate the peculiar nature of this object. SN 2006bt has broad, slowly declining light curves indicative of a hot, high-luminosity SN, but lacks a prominent second maximum in the i band as do low-luminosity SNe Ia. Its spectra are similar to those of low-luminosity SNe Ia, containing features that are only present in cool SN photospheres. Light-curve fitting methods suggest that SN 2006bt is reddened by a significant amount of dust; however, it occurred in the outskirts of its early-type host galaxy and has no strong Na D absorption in any of its spectra, suggesting a negligible amount of host-galaxy dust absorption. C II is possibly detected in our pre-maximum spectra, but at a much lower velocity than other elements. The progenitor was likely very old, being a member of the halo population of a galaxy that shows no signs of recent star formation. SNe Ia have been very successfully modeled as a one-parameter family, and this is fundamental to their use as cosmological distance indicators. SN 2006bt is a challenge to that picture, yet its relatively normal light curves allowed SN 2006bt to be included in cosmological analyses. We generate mock SN Ia datasets which indicate that contamination by similar objects will both increase the scatter of a SN Ia Hubble diagram and systematically bias measurements of cosmological parameters. However, spectra and rest-frame i-band light curves should provide a definitive way to identify and eliminate such objects.
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